There are a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme to compensate errors and to secure reliability of communication. In the case of the FEC scheme, redundant error correction codes are added to information bits to thereby correct errors at a receiving end. The FEC scheme has an advantage in that time delay is low and information separately transmitted and received between a transmitting end and a receiving end is not required; however, it has a disadvantage in that system efficiency is low in a good channel environment. The ARQ scheme may have high transmission reliability; however, it has a disadvantage in that time delay occurs and system efficiency is low in a poor channel environment.
A hybrid automatic repeat request (HARQ) scheme, which is a combination scheme of the FEC scheme and the ARQ scheme, improves performance by confirming whether or not data received in a physical layer includes an error that may not be reproduced and requesting retransmission when the data includes the error.
When the error is not detected in the received data, a receiver transmits a positive acknowledgement (ACK) signal as reception acknowledgement to inform a transmitter that it successfully receives the data. When the error is detected in the received data, the receiver transmits a negative acknowledgement (NACK) signal as the reception acknowledgement to thereby inform the transmitter that it detects the error. When the transmitter receives the NACK signal, it may retransmit the data.
The long term evolution (LTE) based on the 3rd generation partnership project (3GPP) technical specification (TS) release 8 is the leading next generation telecommunication standard.
The 3GPP LTE supports the HARQ in both of uplink transmission and downlink transmission. The downlink HARQ indicates that when a base station transmits downlink data, a user equipment transmits an ACK/NACK signal for the downlink data. The uplink HARQ indicates that when the user equipment transmits uplink data, the base station transmits an ACK/NACK signal for the uplink data.
Discussion on the 3GPP LTE-Advanced (LTE-A), which is advancement of the 3GPP LTE, has been recently conducted. As a newly added representative technology in the LTE-A system, there are carrier aggregation, a relay, and uplink multiple input multiple output (MIMO). The carrier aggregation is used to flexibly extent a usable bandwidth. The relay increases coverage of a cell, supports group mobility, and enables user-centric network disposition. The uplink MIMO increases a data rate by supporting multiple antennas, in contrast with the LTE supporting only a single antenna in the uplink transmission.
A method for improving performance of the HARQ in the 3GPP LTE-A in which a new technology is introduced is suggested.